The present application is based on and claims priority from Japanese Patent Application 2001-302104, filed Sep. 28, 2001, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an AC generator control system for a vehicle, such as a passenger car or a truck.
2. Description of the Related Art
There is an AC generator control system for a vehicle that is provided with a function for controlling the output power of the AC generator to stabilize the idling speed of an engine. On the other hand, it is necessary to measure the output power of such an AC generator accurately as possible in a short time for a delivery inspection. For this purpose, such an output control function has to be invalidated.
JP-A-6-311800 discloses an AC generator control system that has a field-current restricting circuit. When voltage of an L-terminal to which a charge lamp is connected becomes lower than a predetermined voltage, the field-current restricting circuit is disabled.
It is desirable to employ a MOSFET as a switching element of the field-current restricting circuit in view of minimizing electric power loss.
However, such a MOSFET may fail to restrict the field current if the L-terminal voltage is excessively lower than a predetermined voltage. When an electric load is connected and the charge lamp is turned on, the input torque of the AC generator may abruptly increase. As a result, vibration of the engine may increase so much that vehicle speed may decrease.
In addition, a so called IG-terminal with which whether the key switch is turned on or off is detected and a so called L-line connected to the L-terminal are integrated to simplify assembling works. The integration of the IG-terminal and the L-terminal may make the delivery inspection more difficult because the output power control can not be maintained if the L-terminal voltage is lower than a predetermined voltage.
Therefore, the present invention has been made in view of the above problems.
It is a main object of the invention to provide a generator control system for a vehicle that can maintain the output power even when the field-current restricting function is disabled during the delivery inspection.
According to a feature of the invention, a generator control system for a vehicle includes an AC generator having a field coil, a rectifying unit, a switch connected in series with the field coil, a voltage regulator unit, a field-current restricting unit for controlling the switch, a forbidding unit having a command signal input terminal for disabling operation of the field-current restricting unit when a voltage higher than a predetermined regulation voltage is applied to the command signal input terminal. Therefore, whenever a voltage higher than a predetermined reference voltage is applied to the forbidding unit from outside, the field-current restricting unit can be disabled. As a result, accurate delivery inspection of the AC generator can be carried out in a short time.
The forbidding unit may disable the field-current restricting unit when the voltage applied to the command signal input terminal is higher than the predetermined regulation voltage for a period longer than a predetermined period. This prevents erroneous operation of the forbidding unit. The rectifying unit may be comprised of a plurality of zener diodes having a breakdown voltage, and the voltage applied to the command signal input terminal is higher than the breakdown voltage. Therefore, even if a high surge voltage is generated by some electric device, the rectifying unit can absorb the surge voltage, thereby preventing erroneous operation of the generator control system.